Self-assembled monolayers of cavitand receptors for the binding of neutral molecules in water

Resorcin[4]arene cavitands 2-4 were synthesized starting from tetrol 5. With these cavitand tetrasulfides, self-assembled monolayers (SAMs) on gold were prepared and characterized by electrochemical capacitance and resistance measurements, contact angle (CA) measurements, grazing angle FT-IR spectroscopy, and X-ray photoelectron spectroscopy (XPS). In situ surface plasmon resonance (SPR) spectroscopy was employed to study the host-guest interactions at the monolayer-water interface, between receptor adsorbates 1-4 and p-toluic acid, benzoic acid, p-nitrobenzoic acid, p-hydroxybenzoic acid, p-cresol, p-nitrophenol, and p-methoxyphenol. SPR results show that the presence of functional groups on the upper rim of the adsorbate molecules induces selectivity in the guest recognition process. Furthermore, it is interesting to note that such interactions are not directly related to the degree of hydrophobicity of the receptor adsorbate or of the guest. Concentration-dependent experiments were performed with p-nitrophenol as guest for a monolayer of adsorbate 1. At a 3 mM concentration of p-nitrophenol, approximately five to eight guest molecules associate with each adsorbate molecule, implying the formation of 1-4 layers of guests on the receptor surface

Charge-transfer phenomena in novel, dual-component, sugar-based organogels

The synthesis of a new saccharide-based gelator (2) containing a donor moiety has been described. Gelation experiments of a dual-component gel consisting of a saccharide-based gelator bearing an acceptor group (1) and of 2 have been performed in a variety of organic solvents and water. Moreover, gelation tests at different molar ratios of 1 and 2 have been performed in water, octanol, and diphenyl ether. In these last two solvents a gel color change was observed, from colorless to yellow, upon cooling of the sample to room temperature. This phenomenon was further investigated by UV-visible spectroscopy, which revealed the presence of charge-transfer interactions in the gel, in octanol. Temperature-dependence UV spectroscopy confirmed that such interactions occur in the gel but not in the corresponding solution sample. Furthermore, Tgel measurements show that dual-component gels of 1 and 2 present increased thermal stability at a 50:50 ratio of the two gelators, in dependence of the solvent. Transmission electron microscopy (TEM) images of the single-component gels in diphenyl ether revealed that they consist of a fibrous network, while the dual-component gel presents a novel, helical, fibrous-bundle structure

Molecular design of super hydrogelators: understanding the gelation process of azobenzene-based sugar derivatives in water

As an attempt to rationally design aqueous organogelators, a bolaamphiphilic azobenzene derivative (1) bearing two sugar groups was synthesized. Compound 1 formed a gel in water even at concentrations as low as 0.05 wt % (0.65 mM). Spectroscopic studies and electron-micrographic observations have clarified the gel structure and the origin of the gelation ability for water

More than just a catalyst: a novel role for benzylamine in the sol-gel transcription or organogels

Gelator–catalyst interactions allow the transcription of the organogel structure of methyl-4,6-O-(p-nitrobenzylidene)--D-g lucopyranoside (1) into its silica analogue, even in the absence of positive charges or H-bonding sites on the gelator molecule which, until now, were considered indispensable. \u

Organogel or polymer gel; facilitated gelation of a sugar-based organic gel by the addition of a boronic acid-appended polymer

The combination of boronic acid-appended poly(L-lysine) 1 and sugar-based gelator 2 yields a novel organo-polymer gel, consisting of vesicles held together by polymer molecules

Cyclohexane bis-urea compounds for the gelation of water and aqueous solutions

A new class of efficient hydrogelators has been developed by a simple modification of the peripheral substituents of cyclohexane bis-urea organogelators with hydrophilic hydroxy or amino functionalities. These bis-urea hydrogelators were synthesised in two or three steps using an alternative procedure to the common isocyanate method. Gelation was obtained with organic solvents, water and strongly basic aqueous solutions like 25% ammonia. Hydrogelation was found to depend on a delicate balance between the hydrophobicity of the alkyl chains, hydrophilicity of the terminal substituents and the enantiomeric purity of the compound. The hydrogels consisted of a network of fibers, in which all urea groups are involved in intermolecular hydrogen bonding. Most likely, gelation is driven by hydrophobic interactions of the methylene units, whereas hydrogen bond formation between the urea groups provides the necessary anisotropy of the aggregation and the high thermal stability of the gels.